building multi dimensional array

Question

I am trying to build a multi dimensional array with node.js using redis as the data source. I am however not doing it right.

the menuKey contains key containing a sorted set in redis, the sorted set contains values referencing other keys. e.g:

menu:main:sections contains ["menu:main:section1","menu:main:section2"]
menu:main:section1 contains ["option1", "option2"]
menu:main:section2 contains ["option1"]

the array I am trying to build:

[["option1", "option2"], ["option1"]]

This is the code I have but I am placing a callback wrong somehow?

function handleMenu(jsonrpc) {
  var params = jsonrpc['params'];
  var result = [];
  var sections = [];

  menuKey = 'menu:' + params['menu'] + ':sections';
  async.series([
      function (callback) {
        redis.zrevrange(menuKey, 0, -1, function(err, sections) {
          async.forEachSeries(sections, function(section, sectionCallback) {
            redis.zrevrange(section, 0, -1, function(err, items) {
              result.push(items); 
              sectionCallback();
            });
          }, callback);
        });
      }
  ], function() {
    console.log(result);
  });
}

I don't see what I am doing wrong, please advice.

Perhaps what you need is an object instead of an array, plus the syntax looks wrong...["menu:main:section1": ["option1", "option2"] ?? — elclanrs
– elclanrs, Commented Oct 25, 2012 at 23:33
I'm pretty positive that I need a multi dimensional array. And yeah the syntax might be wrong, I'm new to this node.js thing. I'm trying to get array[0][0] = 'a', array[0][1] = 'b', array[1][0] = 'c'. if you get my drift. — user1707250
– user1707250, Commented Oct 25, 2012 at 23:36
If your index is a string, you need an object. If your index is an implicit integer, you need an array. { "prop1" : [ index0, index1 ], "prop2" : [ index0 ] } (quotes around property names are optional in this format) — LetterEh
– LetterEh, Commented Oct 25, 2012 at 23:39
well, what I want is a multi dimensional array, so I might need to use an int index. The reason I use zrevrange is that I want the "sections" to be in order as "ranked" in the sorted redis set and those "sections" should contain the "items" which are references to hashes also in ranked order. I want to return the order of the sections and items in each sections. I will be retrieving the hashes in calls later on. — user1707250
– user1707250, Commented Oct 25, 2012 at 23:52
A multidimensional array would look like array = [ [ index0, index1 ], [ index ] ]. If you want to map "menu:main:section1" -> 0 somehow, and "menu:main:section2" -> 1 go for it. But if you want to say array["menu:main:section1"][0] = "a"; then you're using an object on the outside, and an array as the value of the property. Objects also support int-based prop names, but will suffer a small string-cast (0 -> "0") penalty in most engines, including V8. — LetterEh
– LetterEh, Commented Oct 26, 2012 at 0:01

Waylon Flinn · Accepted Answer · 2012-10-27 21:19:01Z

1

I think you have two problems.

you need a javascript object instead of an array as your top level container
you appear to be overwriting your results at the end

Try this:

function handleMenu(jsonrpc) {
  var params = jsonrpc['params'];
  var result = {}; // THIS LINE IS DIFFERENT
  var sections = [];

  menuKey = 'menu:' + params['menu'] + ':sections';
  async.series([
     function (callback) {
         redis.zrevrange(menuKey, 0, -1, function(err, values) {
         sections = values;
         callback(); 
     });
  },
  function (callback) {
    async.forEachSeries(sections, function(section, cb) {
      redis.zrevrange(section, 0, -1, function(err, values) {
        result[section] = values;
        cb();
      });
    }, callback);
  }
  ], function() {
    // result = sections; // <--- DON'T DO THIS
    console.log(result);
  });
}

In this case result will look like this:

{"menu:main:section1": ["option1", "option2"], "menu:main:section2": ["option1"]}

You don't need a two dimensional array. sections is an ordered index into result. You go through sections in order and use these keys to extract arrays which preserve your secondary order. Like so:

var i = 0,
    j = 0,
    section,
    contents;

for(i = 0; i < sections.length; i++){
    section = sections[i];
    contents = result[section];
    for(j = 0; j < contents.length; j++{
        console.log(contents[j]);
    }
}

UPDATE:

If absolutely have to have a 2D array. Then declare a variable i (and set it to 0) at the top of handleMenu and use it instead of sections, like this:

result[i++] = values;

also, change the result declaration back to this:

var result = [];

edited Oct 27, 2012 at 21:19

answered Oct 26, 2012 at 5:12

Waylon Flinn

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1 Comment

user1707250 Over a year ago

I see now that I've been using results as a hashmap (or object) this was not my intention. I updated the question rewritten to be arrays. The issue still exists. I'm placing a callback wrongly?

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